Minimally invasive surgical techniques have gained significant popularity due to their ability to accomplish desirable outcomes with reduced patient pain and accelerated recovery and return of the patient to normal activities. Arthroscopic surgery, wherein the intra-articular space is filled with fluid, allows orthopedic surgeons to efficiently perform procedures using special purpose instruments designed specifically for arthroscopy. Among these special purpose tools are various manual graspers and biters, powered shaver blades and burs, and electrosurgical devices. During the last several years specialized arthroscopic electrosurgical electrodes referred to in the art as “ablators” have been developed. Examples of such instruments include ArthroWands manufactured by Arthrocare (Sunnyvale, Calif.), VAPR electrodes manufactured by Mitek Products Division of Johnson & Johnson (Westwood, Mass.) and electrodes by Smith and Nephew, Inc. (Andover, Mass.). These ablator electrodes differ from conventional arthroscopic electrosurgical electrodes in that they are designed for the bulk removal of tissue by vaporization rather than the cutting of tissue or coagulation of bleeding vessels. While standard electrodes are capable of ablation, their geometries are generally not efficient for accomplishing this task. The tissue removal rates of ablator electrodes are lower than those of arthroscopic shaver blades, however, electrosurgical ablators are used because they achieve hemostasis (stop bleeding) during use and are able to efficiently remove tissue from bony surfaces. Ablator electrodes are used in an environment filled with electrically conductive fluid.
During ablation, current flows from the ablator into the conductive fluid and heats the fluid to its boiling point. Heating of the conductive fluid is proportional to the density of electrical current flowing from the electrode into the fluid. Regions of high current density will experience higher rates of heating as compared to regions of low current density. In general, regions of high current density occur at the corners and edges of the electrode. Steam bubbles form first at the edges of an ablator but eventually cover virtually the electrode's entire surface. When a steam bubble reaches a critical size, arcing occurs within the bubble and enclosed portion of tissue. A train of sparks occurs within the bubble with the train ending when the bubble grows too large or the tissue enclosed in the bubble is evaporated and conditions within the bubble become unfavorable for sparking.
During ablation, water within the target tissue is vaporized. Because volumes of tissue are vaporized rather than discretely cut out and removed from the surgical site, the power requirements of ablator electrodes are generally higher than those of other arthroscopic electrosurgical electrodes. The efficiency of the electrode design and the characteristics of the Radio Frequency (RF) power supplied to the electrode also affect the amount of power required for ablation. Electrodes with inefficient designs and/or powered by RF energy with poorly suited characteristics will require higher power levels than those with efficient designs and appropriate generators. Because of these factors the ablation power levels of devices produced by different manufacturers vary widely, with some using power levels significantly higher than those commonly used by arthroscopists. Ablator electrode systems from some manufacturers may use up to 280 Watts, significantly higher than the 30 to 70 Watt range generally used by other arthroscopic electrosurgical electrodes.
During arthroscopic electrosurgery, all of the RF energy supplied to the electrode is converted into heat, thereby raising the temperature of the fluid within the joint and the temperature of adjacent tissue. Prior to the introduction of ablator electrodes, the temperature of the fluid within the joint was not of concern to the surgeon. However, due to the higher power levels at which they generally operate and the longer periods of time that they are energized, fluid temperature is a major concern during the use of ablator electrodes. Standard arthroscopic electrosurgical electrodes are usually energized for only brief periods, generally measured in seconds, while specific tissue is resected or modified, or a bleeder coagulated. In contrast, ablator electrodes are energized for longer periods of time, often measured in minutes, while volumes of tissue are vaporized.
The temperature of the fluid within the joint is critical since cell death occurs at 45.degree. C., a temperature easily reached with high-powered ablators if fluid flow through the surgical site is insufficient. Patient injury may result. Such injuries have been documented.
The likelihood of thermal injury is strongly affected by the amount of power supplied to the ablator. This, in turn, is determined by the efficiency of the ablator and the speed with which the surgeon desires to remove tissue. A highly efficient ablator will allow the surgeon to remove tissue at desirably high rates while requiring low levels of power. Under these conditions, the likelihood of thermal injuries is reduced significantly.
Ablator electrodes are produced in a variety of sizes and configurations to suit a variety of procedures. Ablators for use in ankle, wrist or elbow arthroscopy, for instance, are smaller than those used in the knee or shoulder. In each of these sizes, a variety of configurations are produced to facilitate access to various structures within the joint being treated. These configurations differ in the working length of the electrode (the maximum distance that an electrode can be inserted into a joint), in the size and shape of their ablating surfaces and in the angle between the ablating face and the axis of the electrode shaft. Electrodes are typically designated by the angle between a normal to the ablating surface and the axis of the electrode shaft, and by the size of their ablating surface and any associated insulator.
Primary considerations of surgeons when choosing a particular configuration of ablator for a specific procedure are its convenience of use (the ease with which the instrument is able to access certain structures) and the speed with which the ablator will be able to complete the required tasks. When choosing between two configurations capable of accomplishing a particular task, surgeons will generally choose the ablator with the larger ablating surface so as to remove tissue more quickly. This is particularly true for procedures during which large volumes of tissue must be removed. One such procedure is acromioplasty, the reshaping of the acromion. The underside of the acromion is covered with highly vascular tissue that may bleed profusely when removed by a conventional powered cutting instrument, such as an arthroscopic shaver blade. Ablator electrodes are used extensively during this procedure since they are able to remove tissue without the bleeding which obscures the surgeon's view of the site. Ablation in the area under the acromion is most efficiently accomplished using an electrode on which a line normal to the ablating surface is approximately perpendicular to the axis of the ablator shaft. Such an electrode is designated as a “90 Degree Ablator” or a “side effect” ablator. Examples of such electrodes include the “3.2 mm 90 Degree Three-Rib UltrAblator” by Linvatec Corporation (Largo, Fla.), the “90 Degree Ablator” and “90 Degree High Profile Ablator” by Smith and Nephew (Andover, Mass.), the “Side Effect VAPR Electrode” by Mitek Products Division of Johnson and Johnson, and the “3.5 mm 90 Degree Arthrowand”, “3.6 mm 90 Degree Lo Pro Arthrowand”, and “4.5 mm 90 Deg. Eliminator Arthrowand” by Arthrocare Corporation.
Recently ablator electrodes have been configured with a means of aspiration to remove bubbles and debris from the surgical site. During electrosurgery in a conductive fluid environment, tissue is vaporized, thereby producing steam bubbles that may obscure the view of the surgeon or displace saline from the area of the intra-articular space that the surgeon wishes to affect. In the case of ablation (bulk vaporization of tissue), the number and volume of bubbles produced is even greater than when using other electrodes since fluid is continually boiling at the active electrode during use. Ideally, flow through the joint carries these bubbles away; however, in certain procedures this flow is insufficient to remove all of the bubbles. The aspiration means on an aspirating ablator removes some bubbles as they are formed by the ablation process, and others after they have collected in pockets within the joint. The ablator aspiration means is typically connected to an external vacuum source that provides suction for bubble evacuation.
Aspiration on currently available ablator products may be divided into two categories according to their level of flow. High-flow ablators have an aspiration tube, the axis of which is coaxial with the axis of the ablator rod or tube, that draws in bubbles and fluid through its distal opening and/or openings cut into the tube wall near its distal tip. High-flow ablators may decrease the average joint fluid temperature by removing heated saline (waste heat since it is an undesirable byproduct of the process) from the general area in which ablation is occurring. The effectiveness of the aspiration, both for removal of bubbles and for removal of waste heat, will be affected by the distance between the aspiration opening and the active electrode. The distal tip of the aspiration tube is generally positioned several millimeters proximal to the active electrode so as to not to obstruct the surgeon's view of the electrode during use. Decreasing this distance is desirable since doing so will increase the effectiveness of the aspiration; however, this must be accomplished without limiting the surgeon's view or decreasing the ablator's ability to access certain structures during use. Examples of high-flow aspirating ablators systems include the Three Rib-Aspirating ablators by Linvatec Corporation and the 2.3 mm and 3.5 mm Suction Sheaths for the VAPR system by Mitek Products, the sheaths being used with standard VAPR ablation probes.
Arthrex, Incorporated (Naples, Fla.) markets aspirating ablators in which the aspiration port is in the distal-most surface of the device, and the aspiration path runs through the device. These devices have higher flow rates than low-flow ablators, though less than the high-flow models previously herein described.
Low-flow ablators are characterized by the aspiration of bubbles and fluid through gaps in the ablating surfaces of the active electrode, conveying them from the surgical site via means in the elongated distal portion of the device. Because the low-flow aspiration tends to draw hot saline from the active site of a thermal process, current low-flow ablators require increased power to operate as effectively as a non-aspirating or high-flow aspirating ablators. In the case of low-flow ablators, the heat removed is necessary process heat rather than the waste heat removed by high-flow ablators. Because of this, aspirating ablators of the low-flow type generally require higher power levels to operate than other ablators thereby generating more waste heat and increasing undesirable heating of the fluid within the joint. Typical of low-flow aspirating ablators are those produced by Arthrocare and Smith and Nephew.
Each of these types of aspirating ablator electrodes has its drawbacks. In the case of high-flow aspirating ablators, the aspiration tube increases the diameter of the device, thereby necessitating the use of larger cannulae. In the case of low-flow aspirating ablators, aspiration decreases the efficiency of the probes since process heat is removed from a thermal process. This decreased efficiency results in decreased rates of tissue removal for a given power level. In turn, this results in increased procedure times or necessitates the use of higher power levels to achieve satisfactory tissue removal rates. Both increased procedure time and high power level usage are undesirable as they cause increased heating of the fluid at the site and thereby the likelihood of thermal injury to the patient.
U.S. Pat. No. 6,840,937 to Van Wyk discloses an aspirating ablator that minimizes the removal of process heat by placing aspiration ports at a distance from the active electrode, specifically in the distal end of the probe, and in the top surface of the ablator, the top aspiration port being surrounded by the insulator that surrounds the active electrode and the port being displaced a short distance from the active electrode. Aspiration ports positioned in this manner remove debris and aspiration byproducts from regions adjacent to the active electrode rather than through the active electrode in the manner of low-flow ablators thereby minimizing the loss of process heat. However, the construction taught by Van Wyk is not well suited to ablators other than 90-degree ablators, in which the aspirating surface is substantially parallel to the tube axis. The distal portion of the device may be bent to create other angles to the tube axis; however, the bend would be proximal to the distal end assembly and would have a relatively large radius such that the finished product would have to be used with large cannulae, an undesirable condition.
U.S. Pat. No. 7,837,683 to Carmel, et al. (herein incorporated by reference in its entirety) describes an aspirating ablator that has an aspiration port in the center of the active electrode. The aspiration port is surrounded by a tubular portion (i.e., wall) that both restricts flow between protuberances surrounding the port and causes aspiration of liquids from regions above (distal to) the ablating surface. The efficiency of the Carmel ablator is increased since the amount of process heat removed is reduced; however, the construction of the device is somewhat complex. Producing ablators of various angles using the construction suggested by Carmel requires that the distal end of the ablator be bent in the same manner as that of the Van Wyk embodiment. The resulting ablator is again too large to be used in small cannulae.
Many surgical procedures are not performed inside a natural or formed body cavity and as such are not performed on structures submerged under a conductive liquid. In laparoscopic procedures, for instance, the abdominal cavity is pressurized with carbon dioxide to provide working space for the instruments and to improve the surgeon's visibility of the surgical site. Other procedures, such as oral surgery, the ablation and necrosis of diseased tissue, or the ablation of epidermal tissue, are also typically performed in an environment in which the target tissue is not submerged. In such cases, it is necessary to provide a conductive irrigant to the region surrounding the active electrode(s), and frequently also to aspirate debris and liquid from the site. Such irrigant may be applied by a means external to the instrument; however, having an irrigation means internal or attached to the instrument generally provides better control and placement. This is also true for aspiration of fluid and debris. External means may be used for aspiration from the site; however, aspiration through the instrument distal end provides improved fluid control and may, in some cases, draw tissue toward the active electrode thereby enhancing performance. U.S. Pat. No. 7,566,333 to Van Wyk, et al. (herein incorporated by reference in its entirety) discloses an electrosurgical device for use in a dry or semi-dry environment.
Electrosurgical devices having means for irrigating a site, and/or means for aspirating fluid, bubbles and debris from a site are well known. Smith, in U.S. Pat. No. 5,195,959, disclose an electrosurgical device with suction and irrigation. Bales, et al., in U.S. Pat. No. 4,682,596 discloses a catheter for electrosurgical removal of plaque buildup in blood vessels, the catheter having lumens for supplying irrigant to the region of the instrument distal tip and for aspirating debris from the region. Hagen, in U.S. Pat. No. 5,277,696 discloses a high frequency coagulation instrument with means for irrigation and aspiration from the region of the instrument tip. Pao, in U.S. Pat. No. 6,674,499, discloses a coaxial bipolar probe with suction and/or irrigation. Eggers, in U.S. Pat. No. 6,066,134, discloses a method for electrosurgical cutting and coagulation that uses a bipolar probe having means for irrigating and aspirating from the region of the probe distal tip. The Eggers device uses the irrigant flow to provide a return path to a return electrode recessed axially a distance away from the active electrode(s).
As in the case with ablators operating in a fluid filled cavity, for those operating in a dry or semi-dry environment with supplied irrigant, the placement and volume of aspiration flow through an electrosurgical instrument in the region of an active electrode, or even through the active electrode, may adversely affect the performance of the instrument. Electrosurgery, particularly procedures in which tissue is vaporized, is a thermal process. Aspiration which draws fluid through or around the active electrode surfaces draws away process heat, thereby decreasing heating of the conductive irrigant in the region so as to decrease bubble production and ablative arcing. This makes the device less efficient thereby requiring increased power to achieve acceptable performance.
The construction of aspirating ablator distal portions (those distal to the handle) may be divided into two types: complex construction in which power is conducted to the active electrode by wires housed within a tubular distal portion, and simple construction in which the elongated tubular structure conducts power to the active electrode.
Aspirating ablation devices with complex construction have a return electrode attached to the probe, the tubular portion conducting RF energy from the return electrode to the handle assembly, from which it is returned to the generator. This tubular return portion must be electrically isolated from the active electrode and wiring within the tubular portion that conducts power to the active electrode. Additionally, the tubular portion must house a dielectric tube for conducting the aspirated materials from the device distal tip to the handle, and therethrough to an external vacuum supply. Aspiration flow must be isolated from the tubular return structure since the conductive liquid contained in the flow is in contact with the active electrode and therefore at high potential. Ablation devices having complex construction are those from Arthrocare, Smith and Nephew, Mitek division of Johnson and Johnson, and Stryker.
Aspirating ablation devices with simple construction use a return electrode in the form of a dispersive pad that is removably applied to the patient's body remote to the surgical site. The distal portion of these device is a metallic tube, to the distal end of which is mounted an active electrode, the RF energy being conducted to the electrode by the tube. Aspirated materials are conducted from the distal tip of the device to the handle, and therethrough to an external vacuum supply. Because the flow is at the same high potential as the tube, it is not necessary to electrically isolate it from the tube. Typical of aspirating ablators having a simple construction are the Lightwave Suction Ablator by Linvatec, and the 9800 series aspirating ablators by Arthrex.
Ablators having an ablating surface with a normal perpendicular to that of the device axis (“90 degree ablators”) are the most popular configuration with surgeons, however, ablators are produced in a variety of configurations with the normal to the ablating surface inclined to the axis at angles ranging between thirty and ninety degrees. Ablators having a complex construction are formed to each unique angle using components specific to that geometry. For instance, the distal-end components used to create a 90-degree ablator are configured differently from those used to create a 60-degree ablator, which are different from those used to create a 30-degree ablator. Mitek produces a “VAPR-T Side-Effect ablator” and a “VAPR-T Reverse-angled Side-Effect ablator” from the same components, the tubular element being bent proximal to the distal electrode assembly, however, because of the bend in the tube the ablator cannot be inserted into a standard small-diameter cannula frequently used for fluid control in shoulder and knee surgery.
In the case of ablators having simple construction, non-aspirating ablators of various angles of a particular configuration (for example 3.4 mm 30-, 60- and 90-degree) may be constructed using common components. For instance, 30, 60 and 90 degree Ultrablators by Linvatec use a common active electrode component and insulator, the active electrode component being bent to the required angle to create the various products. Similarly, Arthrex 45 and 90 degree small joint and meniscectomy ablators have common active electrode components, the distal ablating surface of the component being beveled at 45 degrees to form the 45-degree ablator. The distal end of the element is bent 45 degrees to create a 90-degree ablator.
Prior art aspirating ablators of simple construction (that is, wherein the RF energy is conducted to the active electrode by the elongated tubular distal element) have an active electrode and distal aspiration path formed by an assembly of at least two elements, generally an active electrode element and an element to provide an aspiration path from the aspiration port to the tubular element. This two-piece construction has two associated disadvantages: first, depending on the specific design, the complexity may increase manufacturing difficulty and cost; and second, the complexity may make it difficult to use common components to produce ablators having a range of angular displacement between ablating surface and tube device axis while maintaining a profile that allows use of the device in small diameter cannulas. For instance, Van Wyk in U.S. Pat. No. 6,840,937, Carmel, et al. in co-pending application Ser. No. 11/431,515, teach aspirating ablators with distal electrode assemblies formed from an electrode element and a tubular element for providing an aspiration path, both elements being of a simple, easy to manufacture design that can be produced at low cost. However, if the assembly is bent in such a way that ablators having a range of angles between the surfaces can be formed with the same components, the resulting profile of the bent devices will be such that they cannot pass through small diameter cannulas. Gallo, et al. in co-pending application Ser. Nos. 11/636,548 and 12/639,644 teaches assemblies of complex, difficult to machine components joined by laser welding. While these ablator assemblies can be bent to some degree to produce ablators having a range of angles between the ablating surfaces and the device axis and with the resulting ablators being able to pass through fairly small cannulas, the cost of manufacturing these assemblies is high.
There is a need for an aspirating ablator having a simple construction in which the aspiration flow removes primarily waste heat rather than process heat; and which is constructed so that a single component or set of components can be used to produce at low cost ablators of various angles which may be used with small cannulae for arthroscopy, or in a semi-dry environment.